1. Field
A scroll compressor is disclosed herein.
2. Background
A scroll compressor is a compressor that includes a fixed scroll having a spiral wrap, and an orbiting scroll that revolves with respect to the fixed scroll, that is, a compressor in which the fixed scroll and the orbiting scroll are engaged with each other. The orbiting scroll revolves with respect to the fixed scroll, thereby reducing a volume of a compression chamber, which is formed between the fixed scroll and the orbiting scroll according to an orbiting motion of the orbiting scroll, thus increasing a pressure of a fluid, which is then discharged through a discharge hole formed at a central portion of the fixed scroll. Such a scroll compressor has a feature in which suction, compression, and discharge of a fluid are successively performed while the orbiting scroll revolves. Accordingly, a discharge valve and suction valve may be unnecessary in principle. Also, as a number of components of the scroll compressor is less in comparison to other types of compressors, the scroll compressor may be simplified in structure and rotate at a high speed. Also, as a variation in torque required for the compression is less in comparison to other types of compressors, and suction and compression successively occur, a relatively small amount of noise and vibration may occur.
Important issues in scroll compressors is leakage and lubrication between the fixing scroll and the orbiting scroll. That is, to prevent a refrigerant from leaking between the fixed scroll and the orbiting scroll, an end of a wrap has to be closely attached to a surface of a head plate to prevent compressed refrigerant from leaking. The “head plate” may refer to a portion that corresponds to a main body of the fixed scroll or the orbiting scroll. That is, ahead plate of the fixed scroll may be closely attached to a wrap of the orbiting scroll, and ahead plate of the orbiting scroll may be closely attached to a wrap of the fixed scroll.
On the other hand, friction resistance has to be minimized so as to allow the orbiting scroll to smoothly revolve with respect to the fixed scroll. However, the leakage may conflict with the lubrication. That is, when the end of the wrap and the surface of the head plate are strongly attached to each other, it may be advantageous with respect to leakage, but friction may increase, increasing damage due to noise and abrasion. On the other hand, when adhesion strength is low, the friction may be reduced, however, a sealing force may decrease, increasing the leakage.
Thus, in the related art, a back pressure chamber having an intermediate pressure, which is defined as a value between a discharge pressure and a suction pressure, may be formed in or at a back surface of the orbiting scroll or the fixed scroll to solve the limitations with respect to sealing and friction reduction. That is, the back pressure chamber, which communicates with a compression chamber having an intermediate pressure of a plurality of compression chambers formed between the orbiting scroll and the fixed scroll, may be formed to allow the orbiting scroll and the fixed scroll to be adequately attached to each other, thereby solving the limitations with respect to the leakage and lubrication.
The back pressure chamber may be formed on a bottom surface of the orbiting scroll or a top surface of the fixed scroll. For convenience of description, the back pressure chamber formed on the bottom surface of the orbiting scroll and the back pressure chamber formed on the top surface of the fixed scroll may be referred to as a “lower back pressure type scroll compressor” and an “upper back pressure type scroll compressor”, respectively. The lower back pressure type scroll compressor has advantages in that the lower back pressure type scroll compressor has a simple structure, and a bypass hole is easily formed. However, as the back pressure chamber is formed on the bottom surface of the orbiting scroll, which performs the orbiting motion, the back pressure chamber may change in configuration and position according to the orbiting motion. As a result, the orbiting scroll may be tilted, causing vibration and noise. In addition, an O-ring provided to prevent the refrigerant from leaking may be quickly worn out. The upper back pressure type scroll compressor has a relatively complicated structure. However, as the back pressure chamber is fixed in configuration and position, the fixed scroll may not be tilted, and sealing of the back pressure chamber may be good.
An example of the upper back pressure type scroll compressor is disclosed in Korean Patent Application No. 10-2000-0037517 (hereinafter, the “'517 Application”) entitled Method for Processing Bearing Housing And Scroll Machine Having Bearing Housing, which is hereby incorporated by reference. FIG. 1 of the '517 Application is a cross-sectional view illustrating an example of an upper back pressure type scroll compressor according to the related art. Referring to FIG. 1, the scroll compressor includes an orbiting scroll disposed on a main frame fixedly installed within a casing, and a fixed scroll engaged with the orbiting scroll. Also, a back pressure chamber is defined on the fixing scroll, and a floating plate to seal the back pressure chamber is disposed to vertically slide along an outer circumference of a discharge passage. A cover is disposed on a top surface of the floating plate to partition an inner space of the compressor into a suction space and a discharge space.
The back pressure chamber communicates with one of the compression chambers, and thus, an intermediate pressure is applied to the back pressure chamber. Also, a pressure may be applied upward to the floating plate and applied downward to the fixed scroll. When the floating plate ascends due to the pressure of the back pressure chamber, an end of the floating plate may contact the cover to seal the discharge space. Also, the fixed scroll may move downward and then be closely attached to the orbiting scroll.
However, in a case of the upper back pressure type scroll compressor, when an operation of the scroll compressor is stopped, an intermediate pressure refrigerant of the back pressure chamber may not be easily discharged toward the compression chamber and a suction-side by an orbiting scroll wrap. In detail, when the operation of the scroll compressor is stopped, the pressure within the scroll compressor may converge to a predetermined pressure (an equilibrium pressure). The equilibrium pressure may be a pressure slightly higher than a suction-side pressure. That is, the refrigerant of the compression chamber and the discharge-side refrigerant may be discharged, and the inside of the compressor may converge to the equilibrium pressure. Then, when the compressor operates again, the compressor may operate while a difference between the equilibrium pressure and a pressure at each position occurs.
It may be necessary to maintain the equilibrium pressure while the refrigerant of the back pressure chamber is discharged to the suction-side. If the refrigerant of the back pressure chamber is not discharged, the fixed scroll may be compressed downward by the pressure of the back pressure chamber, and thus, may be maintained in a state in which the fixed scroll is closely attached to the orbiting scroll.
Also, if the refrigerant of the back pressure chamber is not discharged, the pressure of the back pressure chamber may be maintained at the equilibrium pressure. Accordingly, the floating plate may move upward to contact the cover. As a result, the discharge passage for the discharge-side refrigerant may be blocked, preventing the discharge-side refrigerant from being discharged to the suction-side of the compressor, thereby further pressing the fixed scroll downward.
As described above, when the fixed scroll is pressed to maintain the state in which the fixed scroll is closely attached to the orbiting scroll at a pressure greater than a predetermined pressure, it may be difficult to quickly drive the scroll compressor again. As a result, to quickly drive the scroll compressor again, a high initial torque may be required. When the initial torque increases, noise and abrasion may occur, reducing operation efficiency of the compressor.